Abstract: Synthetic peptides which have the sequence:Q.sup.1 -CO -Ala.sup.2 -Asp.sup.3 -Ala.sup.4 -Ile.sup.5 -Phe.sup.6 -Thr.sup.7 -R.sup.8 -Ser.sup.9 -Tyr.sup.10 -Arg.sup.11 -R.sup.12 -Val.sup.13 -Leu.sup.14 -R.sup.15 -Gln.sup.16 -Leu.sup.17 -Ser.sup.18 -Ala.sup.19 -Arg.sup.20 -R.sup.21 -Leu.sup.22 -Leu.sup.23 -Gln.sup.24 -Asp.sup.25 -Ile.sup.26 -R.sup.27 -R.sup.28 -NH-Q.sup.2wherein Q.sup.1 is an omega or alpha-omega substituted alkyl of the structure: ##STR1## where: ?.phi.! is phenyl; Y is H, --NH.sub.2, CH.sub.3 CONH--or CH.sub.3 NH--; Z is H or CH.sub.3 ; m is 1 or 2; n is 0, 1 or 2; R.sup.8 is Asn, Ser, Gln or Thr; R.sup.12 is Lys or Orn; R.sup.15 is Gly, Ala, or Abu;R.sup.21 is Lys or Orn; R.sup.27 is Met or Nle; R.sup.28 is Ser or Asp; and Q.sup.2 is a lower omega-guanidino-alkyl group having a formula: --(CH.sub.2).sub.p --NH--C(NH.sub.2).dbd.NH wherein p is 2-6, and the pharmaceutically acceptable addition salts thereof with the pharmaceutically acceptable organic or inorganic bases or acids.